Windows Defender Definition Updates no longer appearing/installing

My last Windows Defender definition update appears to have been on May 9, v 1.427.720.0) . I had been getting them typically twice a day... often in the evening I'd find a second one available when Checking Updates.

I was able to do the KB KB5058411 and KB5059200 updates on 5/13.

When I check for updates, it says I'm up-to-date. But nothing comes down for definitions.

I have had the Configure Automatic Updates > Group Policy set to "2 - Notify before downloading and installing any updates" since April 29. It's been working as expected. I reset that to "Not configured" to test. Forced a Group Policy Update - no improvement. Rebooted - no improvement.

Ran the Windows Update Troubleshooter (new style) and it claimed to have found an issue but nothing changed. Rebooted, no improvement.

I checked on the MS site Latest security intelligence updates for Microsoft Defender Antivirus and other Microsoft antimalware - Microsoft Security Intelligence and the last update appears to be 5/15 (today). I downloaded mpam-fe.exe. I ran it "as Administrator " and the little wheel spun for a moment up it didn't do any more than that. No program pop-up, no new definition updates appear in the list (should it when installed this way?). I shut off my A/V and ran it again, no change in what it did or didn't do.

There was one optional update for HP Support listed as available under Optional Updates in Windows Update so I clicked to install it. It installed fine.

I shut off my A/V and Checked Updates - no change.

PS: I don't actually use Defender, I use Avast. But it's still been updating twice a day most days.

PPS: The only other Quality Update since 5/9 was KB5056686 for .Net on 5/11.

I got 2 updates today.

Probably not relevant since it is a different Windows version, but recently I could not update the Microsoft Security Essentials definitions in our Windows 7 computer at work. MSE and Windows Defender in Windows 10/11 get the same definitions. I then searched for Windows updates and sure enough there was a pending security update. Once I installed it the definitions are updated. Probably you can do the same, that is install all available Windows updates and then try to update the Windows Defender definitions again.

I found that after installing a third-party antivirus, Windows defender updates continued for several days, but now I only get Windows Security Platform updates occasionally.

Same for me. This is the last one, same date as you.

Senecio said:

View attachment 134231I found that after installing a third-party antivirus, Windows defender updates continued for several days, but now I only get Windows Security Platform updates occasionally.

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It makes sense. If you have a third-party antivirus, Windows Defender is automatically disabled, so there is no point updating its virus definitions. Update the third-party antivirus instead.

But I let Defender do an occasional scan so updates matter! It seems I turned it off and maybe that's the cause.

@Levitate11 check this setting

I found this link:

spapakons said:

Probably not relevant since it is a different Windows version, but recently I could not update the Microsoft Security Essentials definitions in our Windows 7 computer at work. MSE and Windows Defender in Windows 10/11 get the same definitions. I then searched for Windows updates and sure enough there was a pending security update. Once I installed it the definitions are updated. Probably you can do the same, that is install all available Windows updates and then try to update the Windows Defender definitions again.

Click to expand...

That's a different problem. The legacy MSE for W7 stopped downloading new definitions in Feb 2025, due to a switch in TLS 1.2 support.

You can replace MSE with System Center Endpoint Protection (SCEP) client:
http://wsus.ds.download.windowsupda..._2c54f8168cc9d05422cde174e771147d527c92ba.exe

Same product, different branding. Still supported.

Senecio said:

View attachment 134231I found that after installing a third-party antivirus, Windows defender updates continued for several days, but now I only get Windows Security Platform updates occasionally.

Click to expand...

kelper said:

Same for me. This is the last one, same date as you.

View attachment 134232

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Interesting. Can one or both of you guys download the latest definitions direct from MS, "run" the program (As Administrator) and see what it does. As mentioned, on mine it hums with the little "busy" cursor for a few seconds, then it's gone. No program pop-ups at all. Checking the Definitions shows no change.

Here's the MS page with the links (scroll down) for various OS versions: Latest security intelligence updates for Microsoft Defender Antivirus and other Microsoft antimalware - Microsoft Security Intelligence

spapakons said:

It makes sense. If you have a third-party antivirus, Windows Defender is automatically disabled, so there is no point updating its virus definitions. Update the third-party antivirus instead.

Click to expand...

That thought definitely crossed my mind. Perhaps a later MS update added something to make it check and verify if Defender was active. But it's not the tradition if that's what it's now doing - older versions continued to update whether you were using Defender or not.

I'll see if I can turn Defender back on and watch for changes.

When I re-enabled "allow Defender to do occasional scans", Windows downloaded the latest Defender definitions.

Running mpam-fe.exe isn't going to show up on Windows Update History, simply because WU wasn't involved.

You can confirm if mpam-fe.exe updated your definitions correctly by running this PowerShell command:

The latest version numbers are posted on:
Latest security intelligence updates for Microsoft Defender Antivirus and other Microsoft antimalware - Microsoft Security Intelligence

kelper said:

But I let Defender do an occasional scan so updates matter! It seems I turned it off and maybe that's the cause.

@Levitate11 check this setting

View attachment 134234

Click to expand...

@kelper : Where is that option located?

garlin said:

Running mpam-fe.exe isn't going to show up on Windows Update History, simply because WU wasn't involved.

Click to expand...

I suspected that might be an issue. Does the mpam-fe.exe do anything interesting beyond the spinning cursor when you run it?

garlin said:

You can confirm if mpam-fe.exe updated your definitions correctly by running this PowerShell command:

Code:

Get-MpComputerStatus | Format-List AntivirusSignatureVersion, AntispywareSignatureVersion

The latest version numbers are posted on:
Latest security intelligence updates for Microsoft Defender Antivirus and other Microsoft antimalware - Microsoft Security Intelligence

Click to expand...

Press WIN+I to get to settings. Then , 'Privacy and Security'...'Windows Security'...'Virus and threat protection'...and scroll to the bottom.

kelper said:

Press WIN+I to get to settings. Then , 'Privacy and Security'...'Windows Security'...'Virus and threat protection'...and scroll to the bottom.

Click to expand...

Thanks. They sneak those little tidbits in so subtly that I read right past them.

If this fixes it, please mark thread solved.

kelper said:

If this fixes it, please mark thread solved.

Click to expand...

We'll see... I was able to run a quick scan. No change checking updates but I did try the latest direct download so there's a chance I am up-to-date, post #14 notwithstanding.

I'll see if I get anything in the queue this evening or tomorrow when the next updates come out.

As soon as I ran Windows Update as Admin, it downloaded the latest definitions.

Levitate11 said:

I suspected that might be an issue. Does the mpam-fe.exe do anything interesting beyond the spinning cursor when you run it?

View attachment 134243

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That's strange, you should have some version listed (even if it's out of date).